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        <div>
            <div><h4 class="title">
                <a name="asio.reference.async_read_until.overload8"></a><a class="link" href="overload8.html"
                                                                           title="async_read_until (8 of 12 overloads)">async_read_until
                (8 of 12 overloads)</a>
            </h4></div>
        </div>
    </div>
    <p>
        Start an asynchronous operation to read data into a streambuf until a function
        object indicates a match.
    </p>
    <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="../AsyncReadStream.html"
                                             title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a><span
                class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">Allocator</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">MatchCondition</span><span class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="../ReadToken.html" title="Read token requirements">ReadToken</a> <span
                class="special">=</span> <a class="link"
                                            href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">&gt;</span>
<a class="link"
   href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span
        class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">async_read_until</span><span
                class="special">(</span>
    <span class="identifier">AsyncReadStream</span> <span class="special">&amp;</span> <span class="identifier">s</span><span
                class="special">,</span>
    <span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">basic_streambuf</span><span class="special">&lt;</span> <span class="identifier">Allocator</span> <span
                class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">b</span><span
                class="special">,</span>
    <span class="identifier">MatchCondition</span> <span class="identifier">match_condition</span><span class="special">,</span>
    <span class="identifier">ReadToken</span> <span class="special">&amp;&amp;</span> <span
                class="identifier">token</span> <span class="special">=</span> <a class="link"
                                                                                  href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">constraint</span><span
                class="special">&lt;</span> <span class="identifier">is_match_condition</span><span
                class="special">&lt;</span> <span class="identifier">MatchCondition</span> <span
                class="special">&gt;::</span><span class="identifier">value</span> <span
                class="special">&gt;::</span><span class="identifier">type</span>  <span class="special">=</span> <span
                class="number">0</span><span class="special">);</span>
</pre>
    <p>
        This function is used to asynchronously read data into the specified streambuf
        until a user-defined match condition function object, when applied to the
        data contained in the streambuf, indicates a successful match. It is an
        initiating function for an <a class="link" href="../../overview/model/async_ops.html"
                                      title="Asynchronous Operations">asynchronous
        operation</a>, and always returns immediately. The asynchronous operation
        will continue until one of the following conditions is true:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                The match condition function object returns a std::pair where the second
                element evaluates to true.
            </li>
            <li class="listitem">
                An error occurred.
            </li>
        </ul>
    </div>
    <p>
        This operation is implemented in terms of zero or more calls to the stream's
        async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
        If the match condition function object already indicates a match, this
        asynchronous operation completes immediately. The program must ensure that
        the stream performs no other read operations (such as async_read, async_read_until,
        the stream's async_read_some function, or any other composed operations
        that perform reads) until this operation completes.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h0"></a>
        <span><a name="asio.reference.async_read_until.overload8.parameters"></a></span><a class="link"
                                                                                           href="overload8.html#asio.reference.async_read_until.overload8.parameters">Parameters</a>
    </h6>
    <div class="variablelist">
        <p class="title"><b></b></p>
        <dl>
            <dt><span class="term">s</span></dt>
            <dd><p>
                The stream from which the data is to be read. The type must support
                the AsyncReadStream concept.
            </p></dd>
            <dt><span class="term">b</span></dt>
            <dd><p>
                A streambuf object into which the data will be read.
            </p></dd>
            <dt><span class="term">match_condition</span></dt>
            <dd>
                <p>
                    The function object to be called to determine whether a match exists.
                    The signature of the function object must be:
                </p>
                <pre class="programlisting"><span class="identifier">pair</span><span class="special">&lt;</span><span
                        class="identifier">iterator</span><span class="special">,</span> <span
                        class="keyword">bool</span><span class="special">&gt;</span> <span class="identifier">match_condition</span><span
                        class="special">(</span><span class="identifier">iterator</span> <span
                        class="identifier">begin</span><span class="special">,</span> <span
                        class="identifier">iterator</span> <span class="identifier">end</span><span
                        class="special">);</span>
</pre>
                <p>
                    where <code class="computeroutput"><span class="identifier">iterator</span></code> represents
                    the type:
                </p>
                <pre class="programlisting"><span class="identifier">buffers_iterator</span><span
                        class="special">&lt;</span><span class="identifier">basic_streambuf</span><span class="special">&lt;</span><span
                        class="identifier">Allocator</span><span class="special">&gt;::</span><span class="identifier">const_buffers_type</span><span
                        class="special">&gt;</span>
</pre>
                <p>
                    The iterator parameters <code class="computeroutput"><span class="identifier">begin</span></code>
                    and <code class="computeroutput"><span class="identifier">end</span></code> define the
                    range of bytes to be scanned to determine whether there is a match.
                    The <code class="computeroutput"><span class="identifier">first</span></code> member
                    of the return value is an iterator marking one-past-the-end of the
                    bytes that have been consumed by the match function. This iterator
                    is used to calculate the <code class="computeroutput"><span class="identifier">begin</span></code>
                    parameter for any subsequent invocation of the match condition. The
                    <code class="computeroutput"><span class="identifier">second</span></code> member of
                    the return value is true if a match has been found, false otherwise.
                </p>
            </dd>
            <dt><span class="term">token</span></dt>
            <dd>
                <p>
                    The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
                    token</a> that will be used to produce a completion handler, which
                    will be called when the read completes. Potential completion tokens
                    include <a class="link" href="../use_future.html" title="use_future"><code
                        class="computeroutput"><span class="identifier">use_future</span></code></a>,
                    <a class="link" href="../use_awaitable.html" title="use_awaitable"><code
                            class="computeroutput"><span class="identifier">use_awaitable</span></code></a>,
                    <a class="link" href="../yield_context.html" title="yield_context"><code
                            class="computeroutput"><span class="identifier">yield_context</span></code></a>,
                    or a function object with the correct completion signature. The function
                    signature of the completion handler must be:
                </p>
                <pre class="programlisting"><span class="keyword">void</span> <span
                        class="identifier">handler</span><span class="special">(</span>
  <span class="comment">// Result of operation.</span>
  <span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                            class="identifier">error_code</span><span class="special">&amp;</span> <span
                            class="identifier">error</span><span class="special">,</span>

  <span class="comment">// The number of bytes in the streambuf's get</span>
  <span class="comment">// area that have been fully consumed by the</span>
  <span class="comment">// match function. O if an error occurred.</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span
                            class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
                <p>
                    Regardless of whether the asynchronous operation completes immediately
                    or not, the completion handler will not be invoked from within this
                    function. On immediate completion, invocation of the handler will
                    be performed in a manner equivalent to using <a class="link" href="../post.html" title="post"><code
                        class="computeroutput"><span class="identifier">post</span></code></a>.
                </p>
            </dd>
        </dl>
    </div>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h1"></a>
        <span><a name="asio.reference.async_read_until.overload8.remarks"></a></span><a class="link"
                                                                                        href="overload8.html#asio.reference.async_read_until.overload8.remarks">Remarks</a>
    </h6>
    <p>
        After a successful async_read_until operation, the streambuf may contain
        additional data beyond that which matched the function object. An application
        will typically leave that data in the streambuf for a subsequent async_read_until
        operation to examine.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h2"></a>
        <span><a name="asio.reference.async_read_until.overload8.completion_signature"></a></span><a class="link"
                                                                                                     href="overload8.html#asio.reference.async_read_until.overload8.completion_signature">Completion
        Signature</a>
    </h6>
    <pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">error_code</span><span class="special">,</span> <span
            class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span
            class="special">)</span>
</pre>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h3"></a>
        <span><a name="asio.reference.async_read_until.overload8.remarks0"></a></span><a class="link"
                                                                                         href="overload8.html#asio.reference.async_read_until.overload8.remarks0">Remarks</a>
    </h6>
    <p>
        The default implementation of the <code class="computeroutput"><span
            class="identifier">is_match_condition</span></code>
        type trait evaluates to true for function pointers and function objects
        with a <code class="computeroutput"><span class="identifier">result_type</span></code> typedef.
        It must be specialised for other user-defined function objects.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h4"></a>
        <span><a name="asio.reference.async_read_until.overload8.examples"></a></span><a class="link"
                                                                                         href="overload8.html#asio.reference.async_read_until.overload8.examples">Examples</a>
    </h6>
    <p>
        To asynchronously read data into a streambuf until whitespace is encountered:
    </p>
    <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">buffers_iterator</span><span class="special">&lt;</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span><span
                class="special">::</span><span class="identifier">const_buffers_type</span><span
                class="special">&gt;</span> <span class="identifier">iterator</span><span class="special">;</span>

<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span
                class="special">&lt;</span><span class="identifier">iterator</span><span class="special">,</span> <span
                class="keyword">bool</span><span class="special">&gt;</span>
<span class="identifier">match_whitespace</span><span class="special">(</span><span
                class="identifier">iterator</span> <span class="identifier">begin</span><span
                class="special">,</span> <span class="identifier">iterator</span> <span
                class="identifier">end</span><span class="special">)</span>
<span class="special">{</span>
  <span class="identifier">iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span
                class="identifier">begin</span><span class="special">;</span>
  <span class="keyword">while</span> <span class="special">(</span><span class="identifier">i</span> <span
                class="special">!=</span> <span class="identifier">end</span><span class="special">)</span>
    <span class="keyword">if</span> <span class="special">(</span><span class="identifier">std</span><span
                class="special">::</span><span class="identifier">isspace</span><span class="special">(*</span><span
                class="identifier">i</span><span class="special">++))</span>
      <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span
                class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
  <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span
                class="special">,</span> <span class="keyword">false</span><span class="special">);</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span
                class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">e</span><span
                class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">size_t</span> <span class="identifier">size</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span> <span
                class="identifier">b</span><span class="special">;</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read_until</span><span
                class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span
                class="identifier">b</span><span class="special">,</span> <span
                class="identifier">match_whitespace</span><span class="special">,</span> <span class="identifier">handler</span><span
                class="special">);</span>
</pre>
    <p>
        To asynchronously read data into a streambuf until a matching character
        is found:
    </p>
    <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">match_char</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
  <span class="keyword">explicit</span> <span class="identifier">match_char</span><span class="special">(</span><span
                class="keyword">char</span> <span class="identifier">c</span><span class="special">)</span> <span
                class="special">:</span> <span class="identifier">c_</span><span class="special">(</span><span
                class="identifier">c</span><span class="special">)</span> <span class="special">{}</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span
                class="identifier">Iterator</span><span class="special">&gt;</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span
                class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">,</span> <span
                class="keyword">bool</span><span class="special">&gt;</span> <span class="keyword">operator</span><span
                class="special">()(</span>
      <span class="identifier">Iterator</span> <span class="identifier">begin</span><span class="special">,</span> <span
                class="identifier">Iterator</span> <span class="identifier">end</span><span
                class="special">)</span> <span class="keyword">const</span>
  <span class="special">{</span>
    <span class="identifier">Iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span
                class="identifier">begin</span><span class="special">;</span>
    <span class="keyword">while</span> <span class="special">(</span><span class="identifier">i</span> <span
                class="special">!=</span> <span class="identifier">end</span><span class="special">)</span>
      <span class="keyword">if</span> <span class="special">(</span><span class="identifier">c_</span> <span
                class="special">==</span> <span class="special">*</span><span class="identifier">i</span><span
                class="special">++)</span>
        <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span
                class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
    <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">make_pair</span><span class="special">(</span><span class="identifier">i</span><span
                class="special">,</span> <span class="keyword">false</span><span class="special">);</span>
  <span class="special">}</span>

<span class="keyword">private</span><span class="special">:</span>
  <span class="keyword">char</span> <span class="identifier">c_</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">namespace</span> <span class="identifier">asio</span> <span class="special">{</span>
  <span class="keyword">template</span> <span class="special">&lt;&gt;</span> <span class="keyword">struct</span> <span
                class="identifier">is_match_condition</span><span class="special">&lt;</span><span class="identifier">match_char</span><span
                class="special">&gt;</span>
    <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">boost</span><span
                class="special">::</span><span class="identifier">true_type</span> <span class="special">{};</span>
<span class="special">}</span> <span class="comment">// namespace asio</span>
<span class="special">...</span>
<span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span
                class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">e</span><span
                class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">size_t</span> <span class="identifier">size</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span> <span
                class="identifier">b</span><span class="special">;</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read_until</span><span
                class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span
                class="identifier">b</span><span class="special">,</span> <span
                class="identifier">match_char</span><span class="special">(</span><span class="char">'a'</span><span
                class="special">),</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
    <h6>
        <a name="asio.reference.async_read_until.overload8.h5"></a>
        <span><a name="asio.reference.async_read_until.overload8.per_operation_cancellation"></a></span><a class="link"
                                                                                                           href="overload8.html#asio.reference.async_read_until.overload8.per_operation_cancellation">Per-Operation
        Cancellation</a>
    </h6>
    <p>
        This asynchronous operation supports cancellation for the following <a class="link"
                                                                               href="../cancellation_type.html"
                                                                               title="cancellation_type"><code
            class="computeroutput"><span class="identifier">cancellation_type</span></code></a>
        values:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">terminal</span></code>
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">partial</span></code>
            </li>
        </ul>
    </div>
    <p>
        if they are also supported by the <code class="computeroutput"><span
            class="identifier">AsyncReadStream</span></code>
        type's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
        operation.
    </p>
</div>
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        <td align="left"></td>
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            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
            </p>
            </div>
        </td>
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